/*
 * 	<pre>
 *	EasyPeas.
 *  Copyright (C) 2007 S Owen
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 * 
 * Jul 24, 2007
 * InvocationFactory.java
 * </pre>
 */
package org.easypeas.invocation;

import org.apache.log4j.Logger;
import org.easypeas.EasyPeasConstants;
import org.easypeas.exceptions.InvokerNotFoundException;
import org.easypeas.objectcreation.ObjectCreatorFactory;

/**
 * Factory class that returns an Invoker implementation.<br>
 * The current invoker is only InvokerImpl, but this factory is here to support
 * the ability for future customised Invokers.
 * 
 * 
 * @see Invoker
 * @see InvokerImpl
 * 
 * @author S Owen
 */
public class InvocationFactory {
	@SuppressWarnings("unused")
	private static Logger logger = Logger.getLogger(InvocationFactory.class);

	private static InvocationFactory instance = new InvocationFactory();

	/**
	 * Gets the single instance of InvocationFactory.
	 * 
	 * @return single instance of InvocationFactory
	 */
	public static InvocationFactory getInstance() {
		return instance;
	}

	/**
	 * Returns the invoker. This is defined by the parameter easypeas.invoker in
	 * the web.xml for the servlet.<br>
	 * The default is {@link InvokerImpl}
	 * 
	 * @return the invoker
	 * 
	 * @throws InvokerNotFoundException
	 *             the invoker not found exception
	 */
	public Invoker invoker() throws InvokerNotFoundException {
		String property = System.getProperty(EasyPeasConstants.EASYPEA_INVOKER);
		Invoker result = null;
		if (logger.isDebugEnabled())
		{
			logger.debug("Property defined for:"
					+ EasyPeasConstants.EASYPEA_INVOKER + " = " + property);
		}
		if (property == null) {
			result = new InvokerImpl();
			
		} else {
			try {
				result = (Invoker) ObjectCreatorFactory.getInstance().creator()
						.create(property);
			} catch (Exception e) {
				if (logger.isDebugEnabled())
				{
					logger.debug(
							"Error creating Invoker for class:" + property, e);
				}
				throw new InvokerNotFoundException(
						"Error creating Invoker for class:" + property,
						new InvokerImpl());
			}
		}
		return result;
	}

}
